Manufacture of acetic acid from alcohol



Patented Nov. 27, 1934 UNITED STATES MANUFACTURE OF ACETIC ACID FROMALCOHOL Henri Martin Gninot, Melle, France, assignor to Usines De Melle,Melle, Deux- Sevres, France No Drawing. Application September 5, 1933,Serlal No. 688,258. In France September 16,

Claims.

It is known that there exists a method of estimating alcohol byoxidation by means of potassium bichromate, the alcohol beingquantitatively converted into acetic acid by fixation of the quan- 5tity of oxygen strictly corresponding to the conversion:

In this method of estimation, one contents one- 19 self with determiningthe consumption of oxidizing agent in order to deduce therefrom thealcohol that was present in the liquid treated, without in additionendeavouring to estimate or to isolate the acid that is formed.

On the other hand, it has also been proposed to oxidize alcohol intoacetic acid by electrolysis with leaden anodes (Takayama, J. Soc. Chem.Ind. 1926, No. 9, p. 129 B.) However, under these conditions the yieldof acetic acid does not exceed 20 80%; as for the yield of utilizationof the current, it does not exceed 75%. It is possible to improve theworking a little, especially when the temperature is increased, byoperating in the presence of chromic salts; however, the reaction of thedestruction of the acetic acid under the influence of the current, whichdestruction is more pronounced the greater the concentration of theacid, has a limiting effect on the favourable action of these salts.

9 Moreover, the leaden anodes used for the electrolysis are attackedlittle by little owing to the presence of large quantities of acid inthe solution treated.

According to the present invention, the alcohol is oxidized with almostquantitative yields by I duced and submitting the spent solutioncontaining the reduced salts to the action of electrolysis to bring thesalts back to the desired degree of oxidation in order to enable them toexert a fresh action on the alcohol.

For this purpose, one commences by causing a solution of an oxidizingsalt, as for example potassium bichromate to act upon a hydro-alcoholicsolution so as to have, after the reaction, as small an excess ofoxidizing solution as possible. The dilute acetic solution obtained inthis way is then treated in the cold in an extraction battery of knowntype by a solvent such as ethyl acetate or a mixture of benzene andmethylethyl ketone or any other solvent which is only slightly sensitiveto the action of the small quantity of, oxidizing agent that may remainin solution. In this connection it should be observed incidentally thatethyl acetate does not at first sight appear to be suitable because itis partially oxidized by the bichromate even in the cold; however, thisis not a disadvantage, because, in the courseof the;r.e-'- action, thealcohol that is momentarily liberated by the oxidizing solution isconverted into acetic acid, so that, in order to compensate the lossesof ethyl acetate thus caused, it is sufficient, dur- 66 ing thesubsequent separation of the anhydrous acid by distillation, tore-esterify a fraction of the acid that corresponds to the quantityformed to a minor degree at the expense of the ethyl acetate. 70

In all cases, the extract of acetic acid in the solvent is distilled ,bythe known azeotropic method; the acid is separated in the anhydrous formwhilst the recovered solvent can be repeatedly used indefinitely.

As for the spent aqueous solution leaving the extraction battery, itmay, without disadvantage, contain a small proportion of acetic acid,the latter having the property of resisting sufliciently well in a verydilute, solution the subsequent operations of electrolytic oxidationcarried out with a view to the regeneration of the oxidizing agent(Takayama, Zoc. cit). This possibility of contenting oneself with anexhaustion that is not far advanced and is consequently fairly inexs5pensive forms one of the advantages and one of the features of theinvention.

Thus the aqueous solution, that has been roughly freed from acetic acidand from solvent and that contains chromous salts, is then treated,advantageously by electrolysis, with a view to the regeneration of theoriginal chromic solution. Here also, thanks to the indefinitelyrepeated use of the same batch of oxidizing solution, it is in no wayessential to carry the operation to the end as is usually necessary inthe manufacture of chromates. There is thus obtained a very high yieldof utilization of the oxygen produced by the current, which yield is ofthe order of 95% to 98%.

The solution of chromic acid which is regenerated in this way is thenused again for oxidizing fresh quantities of alcohol and so on. Thesmall quantity of acetic acid, which had originally escaped the actionof the solvent, is wholly in the regenerated chromic solution, so thatthere are finally obtained very high yields of direct conversion ofalcohol into acetic acid. In practice, these yields vary from 90 to 99%.

The alcohol that is used as initial material can, no

without disadvantage, contain certain impurities, such as aldehydes,ethyl acetate, etc., which are converted into acetic acid by oxidation.

It is possible, without departing from the scope of the invention, toapply the method to other a1coholse. g. propyl'alcohol. With the higheralcohols, the molecule is split up and acids of lower molecular weightare obtained. Also instead of potassium bichromate, there may be usedother oxidizing agents which are capable of quantitatively convertingthe alcohols into corresponding acidse. g. potassium permanganate usedin a suitable proportion.

What I claim is:-

1. The method of manufacturing organic acids from alcohols, consistingintreating the alcohol with an oxidizing agent capable of regeneration byelectrolysis, extracting the produced acid by a solvent, regeneratingthe residual spent oxidizing agent by electrolysis for re-use, andseparating the acid-solvent mixture into acid and solvent.

2. The method of manufacturing organic acids from alcohols, consistingin treating the alcohol with an oxidizing agent capable of regenerationby electrolysis, extracting the produced acid by a solvent, regeneratingthe residual spent oxidizing agent by electrolysis, re-using theregenerated agent in the process, separating the acid-solvent mixture byazeotropic distillation into acid and solvent, and re-using therecovered solvent in the process.

3.- The method of manufacturing organic acids from alcohols, consistingin treating the alcohol with an aqueous solution of a bichromate salt,extracting the produced acid by a solvent not materiallyafiected by saidsalt, regenerating the residual spent salt solution by electrolysis forreuse, and separating the acid-solvent mixture by azeotropicdistillation into acid and solvent and re-using the recovered solvent inthe process. 4. The method of maufacturing organic acids from alcohols,consisting in treating the alcohol withan aqueous-solution of abichromate salt, extracting the produced acid by ethyl acetate,regenerating the residual spent salt solution by electrolysis for re-useand separating the acid from the ethyl acetate by azeotropicdistillation and re-using the latter in the process.

5. The method of manufacturing organic acids from alcohols, consistingin treating the alcohol with an aqueous solution of a biohromate salt,extracting the produced acid by a mixture of benzene and methylethylketone, regenerating the residual spent salt solution by electrolysisfor reuse and separating the acid from said mixture by azeotropicdistillation and re-using the mixture in the process.

' 6. The method of manufacturing acetic acid from ethyl alcohol,consisting in treating the alcohol with an oxidizing agent capable ofregeneration by electrolysis, extracting the produced acid by a solvent,regenerating the residual spent agent by electrolysis for re-use andseparating the acidsolvent mixture into acid and solvent.

7. The method of manufacturing acetic acid from ethyl alcohol,consistingin treating the alcohol' with an aqueous solution of abichromate salt, extracting the acetic acid by a solvent, regeneratingthe spent salt solution by electrolysis, separating the acetic acid fromthe solvent by azeotropic distillation and re-using the latter in theprocess.

8. The method of manufacturing acetic acid from ethyl alcohol,consisting in treating the alcohol with an aqueous solution of abichromate salt, extracting the acetic acid by ethyl acetate,regenerating the spent salt solution by electrolysis, re-

using the regenerated solution in the process, separating the aceticacid from the ethyl acetate by azeotropic distillation, and re-using therecovered ethyl acetate in the process.

9. The method of manufacturing acetic acid from ethyl alcohol,consisting in treating the alcohol with an aqueous solution of abichromate salt, extracting the acetic acid by a mixture of benzene andmethylethyl keto'ne, regenerating the spent salt solution byelectrolysis, re-using the regenerated solution in the process,separating the acetic acid from the benzene and methylethyl ketone byazeotropic distillation, and reusing the recovered benzene andmethylethyl ketone in the process.

10. The method of manufacturing acetic acid from ethyl alcohol,consisting in treating the alcohol with an aqueous solution of oxidizingagent capable of regeneration by electrolysis, roughly extracting theproduced acetic acid by a solvent not materially affected by saidoxidizing agent, separating the acid from the solvent by azeotropicdistillation, regenerating by electrolysis the spent oxidizing agentcontaining any unextracted acid,

and re-using the regenerated agent together with said unextracted acidin the process;

HENRI MARTIN GU'INOT.

